Sequence generation and transmission method based on time and frequency domain transmission unit

ABSTRACT

A method and a user equipment for transmitting control information in a communication system are discussed. The method according to an embodiment includes multiplying a transmission information symbol s for the control information by a frequency direction sequence c(k) to generate a first output sequence s(k), where s(k)=s*c(k), k=0, . . . , N k −1, and N k  corresponds to a number of subcarriers included in a resource block allocated for an uplink control channel; multiplying the first output sequence s(k) by a time direction sequence x(n) to generate a second output sequence s(k, n), where s(k, n)=s(k)*x(n), n=0, . . . , N n −1, and N n  corresponds to a number of symbols used for transmission of the control information in a transmission time interval; and transmitting the second output sequence s(k, n) through the uplink control channel in the transmission time interval.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 14/563,787 filed on Dec. 8, 2014, which is a Continuation ofU.S. patent application Ser. No. 13/538,906 filed on Jun. 29, 2012 (nowU.S. Pat. No. 8,929,194 issued on Jan. 6, 2015), which is a Continuationof U.S. patent application Ser. No. 12/520,108 filed on Jun. 19, 2009(now U.S. Pat. No. 8,228,782 issued on Jul. 24, 2012), which is filed asthe National Phase of PCT/KR2007/006733 filed on Dec. 21, 2007, whichclaims the benefit under 35 U.S.C. §119(e) to U.S. ProvisionalApplication Nos. 60/912,109 filed on Apr. 16, 2007, 60/886,621 filed onJan. 25, 2007, and 60/871,604 filed on Dec. 22, 2006, and under 35U.S.C. §119(a) to Korean Patent Application Nos. 10-2007-0062893 filedon Jun. 26, 2007, 10-2007-0036460 filed on Apr. 13, 2007, and10-2007-0032725 filed on Apr. 3, 2007, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for transmitting/receiving asignal for use in a mobile communication system, and more particularlyto a method for generating/transmitting a sequence based on atime-frequency domain transmission unit.

Discussion of the Related Art

The present invention relates to a method for modulating a predeterminedtransmission sequence in time and frequency directions at intervals of atransmission unit, generating a symbol acquired by the modulation of thepredetermined transmission sequence, and transmitting the symbol atintervals of a transmission unit.

In a Universal Mobile Telecommunications System (UMTS) communicationsystem based on the 3rd Generation Partnership Project Long TermEvolution (3GPP LTE) scheme, a transmission end defines a TransmissionTime Interval (TTI) used as a time unit capable of simultaneouslytransmitting at least one transmission block (i.e., upper layertransmission information). In the case of small-sized packet data suchas VoIP, a slot contained in a single TTI (i.e., 1 TTI) is defined as aunit for simultaneously transmitting corresponding information. Aplurality of OFDM symbols may be contained in the above-mentioned TTI ina time direction, the 3GPP LTE assumes that 14 OFDM symbols arecontained in the 1 TTI and two slots are contained in the 1 TTI. ThisTTI definition is changed according to system categories. The presentinvention aims to define a format for transmitting a packet or controlsignal when a predetermined transmission unit is defined in a generalwireless communication system.

In the meantime, the transmission unit may be adjusted in OFDM-lengthunits on a time axis. In the case of establishing a transmission unitreference, a coverage and energy efficiency are considered. For example,a Single-Carrier Frequency Division Multiplexing (SC-FDM) scheme used asan uplink transmission scheme associated with a control signal for usein the 3GPP LTE scheme will hereinafter be described.

The most important duty of a User Equipment (UE) or terminaltransferring a control signal to a Node-B is the coverage. In otherwords, although a bandwidth of a transmission (Tx) signal of the userequipment (UE) is not relatively large, the power must be concentratedon a single place and be transmitted to this place, and it is preferablethat a variable width (PAPR) of the transmission signal may be narrow.For these purposes, the 3GPP LTE has prescribed that the SC-FDM schemeis basically used as an uplink signal transmission scheme.

FIG. 1 is a block diagram illustrating a transmission end of aconventional communication system based on the SC-FDM scheme.

The SC-FDM scheme is a transmission scheme for improving PAPRcharacteristics by reducing the amount of change in a signal. In thecase of using the same power amplifier, a wider coverage can beimplemented. As can be seen from the transmission end based on theSC-FDM scheme of FIG. 1, the most important characteristic of the SC-FDMscheme is that a transmission (Tx) signal is firstly spread out by a DFTmodule 101 according to the DFT scheme. This spread signal is mapped tothe transmission (Tx) signal based on the OFDM symbol unit by an IFFTmodule 102 serving as an IDFT module.

Therefore, the transmission (Tx) signal is concentrated on atransmission frequency band, and is then transmitted to a destination.The resultant signal has the same effect as in the case in which thetransmission (Tx) signal is transmitted via a single-carrier.

In the meantime, the transmission signal proposed by the 3GPP LTE schemeemploying the SC-FDM scheme basically transmits information using asingle OFDM symbol unit.

However, a transmission unit capable of actually transmitting apredetermined amount of information at once is a TTI or slot, so that itis preferable that the transmission (Tx) signal is constructed on thebasis of the TTI or slot. A control signal proposed by the 3GPP LTE doesnot clearly provide a method for supporting a multi-format or acquiringvarious spreading gains, or a method for increasing the number of userequipments (UEs).

Specifically, in the case where the same user transmits differentamounts of control signals, a control channel structure capable ofeasily supporting the above-mentioned control signals is required.However, no solution capable of implementing the control channelstructure has been proposed.

The present invention provides an improved channel structure fortransmitting a control signal. This improved channel structure can beapplied to uplink/downlink channels based on a predeterminedcommunication scheme capable of transmitting a signal via apredetermined sequence, and has no problem in a multi-cell deployment.

The present invention provides a method for guaranteeing a maximumnumber of sequences which can be applied to a corresponding channel viaa channel structure, and transmitting/receiving a signal using theguaranteed sequences.

For these purposes, in the case of designing a control signal for use ina predetermined communication system, the present invention mustconsider a method for generating/transmitting a control signal using auser equipment (UE).

Provided that neighboring cells use the same sequence or the same uplinkresources in a multi-cell environment, an unexpected collision may occurbetween the neighboring cells.

In order to discriminate between the neighboring cells, the neighboringcells may use different resources according to a predetermined ruleprescribed between them. However, this method may have difficulty in acell planning of an actual system deployment stage.

In the meantime, for example, the above-mentioned communication systemmay consider a method for implementing a randomization effect accordingto a frequency hopping- or sequence hopping-scheme. In this case, theabove-mentioned randomization effect method accommodates interferencebetween different cells without any change, so that it isdisadvantageous to the system.

Therefore, the best solution for solving the above-mentioned problems isto differently use different user equipments (UEs) according to the CDMscheme using different orthogonal sequences or other sequences similarto the orthogonal sequences.

The above-mentioned solution has no need to perform the cell planning,and allows different systems to share the same resources with minimumcosts. A proper number of spread sequences are required for theabove-mentioned solution. However, in fact, the conventional art doesnot provide a method for employing a sufficient number of sequenceswithout deteriorating a sequence performance.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a sequence generationand transmission method based on time/frequency domain transmission unitthat substantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method for modulatingtransmission information in TTI or slot units instead of symbol units,generating a corresponding transmission unit symbol using the modulatedinformation, and transmitting a signal using the generated transmissionunit symbol. The above-mentioned method can be applied to a controlchannel for transmitting a control signal to an uplink.

Another object of the present invention is to provide a method forsimultaneously transmitting a uniformity (PAPR/CM) of a transmission(Tx) signal, a cell coverage, and much more information.

Yet another object of the present invention is to provide a transmissionsignal generation method for supporting a multi-format or acquiring avariety of spreading gains.

Yet another object of the present invention is to provide a method forminimizing an interference between UE signals while simultaneouslyincreasing the number of UEs, and allowing a user to transmit variousamounts of signals.

Yet another object of the present invention is to provide a channelstructure for guaranteeing a maximum number of available sequences, andtransmitting/receiving a signal using the channel structure.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for modulating a predetermined transmission sequence in time andfrequency directions within transmission units of time/frequency domainin a communication system, and generating a transmission-unit-basedsymbol is presented. In one embodiment of this method, the methodcomprises: modulating the predetermined transmission sequence in a firstdirection corresponding to either one of the time and frequencydirections in transmission units of a time- or frequency-domaincorresponding to the first direction, and generating a first-directionmodulation sequence; and modulating the first-direction modulationsequence in a second direction corresponding to the other one of thetime and frequency directions in transmission units of the time- orfrequency domain corresponding to the second direction, and generatingthe transmission-unit-based symbol.

Preferably, the time-domain transmission unit is either a transmissiontime interval (TTI) or a slot contained in the transmission timeinterval (TTI).

Preferably, the first-direction modulation and the second-directionmodulation indicate either a spreading or a scrambling of thepredetermined sequence.

Preferably, the first direction-direction modulation is performed suchthat the predetermined transmission sequence is multiplied by atime-direction modulation sequence having a predetermined length of thetime-domain transmission unit; and the second direction-directionmodulation is performed such that each symbol of the first-directionmodulation sequence is multiplied by a frequency-direction modulationsequence having a predetermined length corresponding to the number ofsub-carriers contained in a single resource block.

Preferably, the first-direction modulation is performed such that thepredetermined transmission sequence is multiplied by afrequency-direction modulation sequence having a predetermined lengthcorresponding to the number of sub-carriers contained in a singleresource block; and the second direction-direction modulation isperformed when the first-direction modulation sequence for each symbolof the time-domain transmission unit is multiplied by a time-directionmodulation sequence having a predetermined length of the time-domaintransmission unit.

Preferably, the method further comprising: performing a frequencyhopping on each predetermined symbol contained in the time-domaintransmission unit at the transmission-unit-based symbol.

Preferably, the communication system is a single-carrier frequencydivision multiplexing (SC-FDM)-based communication system, and thepredetermined transmission sequence is a sequence in which heterogeneouscontrol information is mixed by a Discrete Fourier Transform (DFT)spreading.

In another aspect of the present invention, there is provided a methodfor transmitting a control signal in a communication system whichallocates a predetermined number of sub-carrier areas for a controlchannel. In one embodiment for this aspect, the method comprises: a)masking a symbol unit based predetermined sequence in each symbolcontained in a time-domain transmission unit, in the predeterminednumber of sub-carrier areas allocated for the control channel; and b)transmitting the symbol-masked sequence per the time-domain transmissionunits.

Preferably, the predetermined number of sub-carrier areas allocated forthe control channel are located at one or both ends of a systembandwidth.

Preferably, the predetermined number of sub-carrier areas allocated forthe control channel are allocated to the same frequency band within acell of a neighboring group.

Preferably, the predetermined number of sub-carrier areas allocated forthe control channel is distributedly arranged in a system bandwidth.

Preferably, the masking step a) includes: applying a symbol-unit basedcyclic shift to the symbol-unit based sequence, and performing a maskingthereon.

Preferably, the symbol-unit based sequence is generated by a firstprocess and a second process, the first process is modulating apredetermined input sequence in a first direction corresponding toeither of time and frequency directions within transmission units of atime- or frequency-domain corresponding to the first direction, andgenerates a first-direction modulation sequence, and the second processis modulating the first-direction modulation sequence in a seconddirection corresponding to the other one of the time and frequencydirections in transmission units of a time- or frequency-domaincorresponding to the second direction.

Preferably, at least one of an index of the symbol-masked sequence and asymbol-unit based cyclic shift applied to the symbol-masked sequence isindicative of control information.

Preferably, the method further comprising: c) inserting a pilot into apredetermined number of symbols, the predetermined number of symbolscorresponds to a number of difference between the number of symbolscontained in the time domain transmission unit and a prime number lessthan the number of the symbols contained in the time domain transmissionunit.

Preferably, the inserting step c) includes: inserting pilots, into thecenter part of a domain to be channel-estimated such that the insertedpilots are equally spaced apart from each other.

Preferably, a first area contained in the time-domain transmission unitsupports a coherent searching scheme; and a second area contained in thetime-domain transmission unit supports a non-coherent scheme, andwherein, in the first area, at least one of an index of a sequencemasked in a symbol contained in the first area, and a symbol-unit basedcyclic shift applied to the sequence masked in the symbol contained inthe first area is indicative of control information, and in the secondarea, symbol information of a sequence masked in a symbol contained inthe second area is indicative of control information.

Preferably, the sequence masked in each symbol contained in thetime-domain transmission unit is indicative of control informationcapable of being searched by a coherent searching process, and a pilottransmission symbol contained in the time domain transmission unittransmitting the control information is arranged at the same position asthat of a pilot transmission symbol of a data transmission channel.

Preferably, the sequence masked in each symbol contained in thetime-domain transmission unit is indicative of control informationcapable of being searched by a coherent searching process, in which thecontrol information is represented by the combination of a sequence foruse in the first-direction modulation of the input sequence and theother sequence for use in the second-direction modulation of the inputsequence.

Preferably, the sequence masked in each symbol contained in thetime-domain transmission unit is indicative of control informationcapable of being searched by a non-coherent searching process, in whichthe control information is represented by a differential modulation ineither the time domain or the frequency domain of the sequence masked ineach symbol.

In yet another aspect of the present invention, there is provided asignal generation method comprising: a) spreading an information symbolin a first domain corresponding to either a frequency domain or a timedomain in symbol units; b) modulating the symbol-unit-spread informationsymbol in the first domain, and generating a first-domain modulationsymbol; and c) modulating the first-domain modulation symbol in a seconddomain corresponding to the other one of the time and frequency domains,and generating a transmission signal.

Preferably, at the spreading step a), a symbol-unit spreading gain ofthe information symbol is proportional to a Quality of Service (QoS)level required for the information symbol.

Preferably, the generating step b) for generating the first-domainmodulation symbol includes: multiplexing the symbol-unit-spreadinformation symbol; and modulating the multiplexed information symbol inthe first domain, and the generating step c) for generating thetransmission signal includes: multiplexing the second-domain modulationsequence in the second domain; and performing the second-domainmodulation on the first-domain modulation symbol using the multiplexedsecond-domain modulation sequence.

Preferably, the method further comprises: if the size of a channel fortransmitting the transmission signal is fixed, applying at least one ofa channel coding, a spreading, and a rate-matching to either controlsignals of different sizes or data of different sizes, such that theinformation symbol has a predetermined size.

Preferably, the information symbol is generated by a control-channelspecific spreading to remove an interference between signals ofdifferent user equipments (UEs), and is then generated.

In yet another aspect of the present invention, there is provided asignal transmission method comprising: dividing sub-carriers containedin a predetermined number of resource blocks (RBs) into a predeterminednumber of channels such that each of the channels includes a primenumber of sub-carriers; and transmitting a signal over the dividedchannels.

Preferably, the signal transmitted over the predetermined number ofchannels is represented by a predetermined sequence, and wherein thepredetermined sequence is a sequence among which a number of distinctivesequence is maximized, if the predetermined sequence has a prime-numberlength.

Preferably, the predetermined sequence is a Constant Amplitude Zero AutoCorrelation (CAZAC) sequence.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

A method for generating/transmitting a sequence based on atime/frequency domain transmission unit according to one embodiment ofthe present invention performs time/frequency direction modulation inpredetermined transmission units (e.g., TTIs or slots) instead of symbolunits, generates a symbol according to the modulated result, andtransmits the generated symbol, so that it can transmit much moreinformation to a desired destination.

Also, the present invention performs masking of a transmission sequenceon a time domain, and transmits the masking-resultant sequence. As aresult, a CAZAC sequence is able to apply a symbol-unit cyclic shift tothe time domain, so that much more information can be transmitted to adesired destination.

As described above, the present invention controls the symbol-unitcyclic shift of the time domain to indicate different controlinformation, so that it can support a non-coherent searching process. Inthe case of using a method for supporting a coherent searching process,the present invention properly adjusts symbols associated with a pilotto guarantee an available number of sequences, and can greatly improve achannel estimation performance.

The present invention applies the above-mentioned method to a controlchannel capable of transmitting only a control signal excepting data, sothat it does not affect signal uniformity and can effectively transmitcontrol information.

In the meantime, a method for generating/transmitting a multi-formatsupporting sequence according to another embodiment of the presentinvention can generate a transmission (Tx) signal to which a variety offormat signals can be applied, can effectively reduce an inter-cellinterference between users (i.e., UEs), and can generate a transmissionsignal for satisfying different service quality levels.

The present invention provides a transmission method based on a sequenceof a prime-number length. In the case of transmitting a control signalwithout using data in an uplink SC-FDM-based communication system, theabove-mentioned transmission method can guarantee a maximum number ofavailable sequences, and at the same time can transmit/receive a signalwithout deteriorating unique characteristics of the sequences.

In other words, in order to perform the multi-cell operation, a maximumnumber of sequences must be provided. For these purposes, the presentinvention provides a method for generating a channel (i.e., a controlchannel) having a prime-number length, and transmitting/receiving asignal using a sequence having the prime-number length.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a block diagram illustrating a transmission end of aconventional SC-FDM-based communication system;

FIG. 2 is a flow chart illustrating a method for generating atransmission unit symbol according to one embodiment of the presentinvention;

FIG. 3 is a structural diagram illustrating a channel structure for usein a specific case in which only a control signal excepting data istransmitted;

FIG. 4 is a structural diagram illustrating a channel structure for usein a specific case in which data and a control signal are simultaneouslytransmitted;

FIG. 5 is a conceptual diagram illustrating a method for generating aTTI-unit symbol modulated in time and frequency directions according toa sequence modulation scheme;

FIGS. 6 and 7 are conceptual diagrams illustrating a variety of methodsfor applying the hopping to the TTI-unit symbol of FIG. 5 according tothe present invention;

FIG. 8 is a conceptual diagram illustrating a method for generating theTTI-unit symbol modulated in time and frequency directions according toa direct modulation scheme according to another embodiment of thepresent invention;

FIG. 9 is a flow chart illustrating a method for transmitting a TTI-unitsymbol according to one embodiment of the present invention;

FIG. 10 is a conceptual diagram illustrating a method for performing atime-domain modulation on a transmission symbol in TTI units, andtransmitting the modulated symbol according to one embodiment of thepresent invention;

FIGS. 11 to 14 are conceptual diagrams illustrating a variety of methodsfor applying the hopping to a transmission format shown in FIG. 11according to the present invention;

FIGS. 15 to 17 are conceptual diagrams illustrating method for insertinga pilot into a TTI-unit symbol based on a coherent scheme according toone embodiment of the present invention;

FIGS. 18 and 19 are conceptual diagrams illustrating methods for merginga coherent-based channel with a non-coherent-based channel, and usingthe merged result according to embodiments of the present invention;

FIG. 20 is a conceptual diagram illustrating a method for spreading aninformation symbol in symbol units in a frequency domain, performing amodulation process in each domain by multiplexing atime/frequency-domain modulation/masking sequence, and transmitting atransmission (Tx) signal according to the modulated result;

FIG. 21 is a conceptual diagram illustrating a method for spreading aninformation symbol in symbol units in a time domain, performing amodulation process in each domain by multiplexing atime/frequency-domain modulation/masking sequence, and transmitting atransmission (Tx) signal according to the modulated result;

FIG. 22 shows an example for applying control signals of various formatswhen the size of a control signal channel is fixed according to oneembodiment of the present invention;

FIG. 23 is a conceptual diagram illustrating a method for defining aspread format based on a control signal format within each UE accordingto the present invention;

FIG. 24 is a conceptual diagram illustrating a sequence generationmethod according to a truncated-sequence generation method;

FIG. 25 is a conceptual diagram illustrating a method for generating asequence according to a padding-sequence generation scheme;

FIG. 26 shows an exemplary structure in which controls channels causedby a resource block division are arranged at both ends of a systembandwidth on a one-to-one basis according to one embodiment of thepresent invention;

FIG. 27 shows an exemplary structure in which a control channel causedby a resource block division is arranged at one end of a systembandwidth according to one embodiment of the present invention;

FIG. 28 shows an exemplary structure in which a predetermined number ofresource blocks are arranged at both ends of a system bandwidth and acontrol channel is formed by division of the resource blocks accordingto one embodiment of the present invention; and

FIG. 29 shows an exemplary structure in which a predetermined number ofresource blocks are grouped into several groups at both ends of a systembandwidth, the resultant groups are arranged at the both ends of thesystem bandwidth, and a control channel is formed by division of theresource blocks according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Prior to describing the present invention, it should be noted that mostterms disclosed in the present invention correspond to general termswell known in the art, but some terms have been selected by theapplicant as necessary and will hereinafter be disclosed in thefollowing description of the present invention. Therefore, it ispreferable that the terms defined by the applicant be understood on thebasis of their meanings in the present invention.

For the convenience of description and better understanding of thepresent invention, general structures and devices well known in the artwill be omitted or be denoted by a block diagram or a flow chart.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

As described above, one embodiment of the present invention provides amethod for modulating transmission information in TTI or slot unitsinstead of symbol units, generating a corresponding transmission unitsymbol using the modulated information, and transmitting a signal usingthe generated transmission unit symbol.

Firstly, a basic embodiment provides a method for generating atransmission unit symbol, and a detailed description thereof willhereinafter be described.

In the case of generating a transmission signal in TTI or slot units,instead of OFDM symbol units, the present invention modulates thetransmission signal not only in a time direction within a singletransmission unit including several OFDM symbols, but also in afrequency direction concerning the generated symbols, so that thetransmission signal may include additional information.

FIG. 2 is a flow chart illustrating a method for generating atransmission unit symbol according to one embodiment of the presentinvention.

Referring to FIG. 2, a predetermined sequence indicating a transmissionsignal is modulated in either a time direction or a frequency directionat step S201. For the convenience of description and betterunderstanding of the present invention, the selected direction is calleda first direction.

If the above-mentioned first-direction modulation is a time-domainmodulation, the sequence indicating the transmission signal ismultiplied by a time-direction modulation sequence having the length ofan OFDM symbol contained in a transmission unit (e.g., 1 TTI or 1 slot)of a corresponding system, so that the sequence modulation in the timedomain is implemented.

If the above-mentioned first-direction modulation is a frequency-domainmodulation, the sequence indicating the transmission signal ismultiplied by a frequency-direction modulation sequence having apredetermined length corresponding to the number of sub-carriersrequired for transmitting conventional single unit information, so thatthe sequence modulation in the frequency domain is implemented.

In this case, the time-direction modulation indicates that apredetermined transmission sequence is spread or scrambled in the timedirection. The frequency-direction modulation indicates that apredetermined transmission sequence is spread or scrambled in thefrequency direction.

If a transmission sequence is a CAZAC sequence, the first-directionmodulation sequence may be an exponential-function sequence for applyinga cyclic shift to the transmission sequence in the same or differentdomains. The first-direction modulation sequence may also be apredetermined modulation sequence.

Therefore, a first-direction sequence is generated at step S202. Inother words, the first-direction sequence indicates that thetransmission sequence is modulated in either the time direction or thefrequency direction.

Thereafter, the first-direction sequence generated at step S202 ismodulated in the other direction, instead of the above-mentioned firstdirection, from among the time and frequency directions. For theconvenience of description and better understanding of the presentinvention, the selected direction is called a second direction.

In the case of the second-direction modulation, if the first-directionsequence generated at step S202 is multiplied by a second-directionmodulation sequence, the second-direction modulation can be implementedin the same manner as in the above-mentioned second-directionmodulation.

In this case, the second-direction modulation sequence has the length ofan OFDM symbol contained in a time domain within the 1 TTI or 1 slot, orhas a predetermined length corresponding to the number of sub-carriersrequired for transmitting conventional single unit information.

Therefore, the time/frequency-direction modulation symbol based on unitsof a transmission time (e.g., TTI or slot) is generated at step S204.So, the present invention can transmit not only information of atransmission sequence but also additional information in a modulationstep for each domain.

For example, if the CAZAC sequence is used as a transmission sequence,two sequences based on different cyclic shifts are allocated toindividual user equipments (UEs), so that the individual UEs canindicate ACK/NACK information.

In this case, different cyclic shifts may be directly applied to aprocess for transmitting the transmission sequence. However, in the caseof using the transmission unit symbol of the present invention, thedifferent cyclic shifts may also be applied to a method for performing atime-domain modulation or a frequency-domain modulation on atransmission sequence.

In association with FIG. 2, the term “transmission unit” may include allof time units (e.g., TTIs and slots), each of which can simultaneouslytransmit transmission information.

For the convenience of description and better understanding of thepresent invention, it is assumed that the above-mentioned transmissionunit is set to the TTI in the present invention. However, it should benoted that the scope of the transmission unit is not limited to the TTI,and can also be applied to other examples as necessary.

In the meantime, the above-mentioned scheme of FIG. 2 can be applied toa control channel for transmitting a control signal to an uplink basedon the SC-FDM scheme, so that the present invention can transmituniformity of a transmission signal, a cell coverage, and more controlinformation at the same time. In association with the above-mentioneddescription, a channel structure used for transmitting a control signalusing the SC-FDM scheme will hereinafter be described in detail.

In the case of transmitting the control signal using the SC-FDM scheme,the following factors must be considered.

Firstly, the present invention must determine the presence or absence ofdata in the transmitted control signal, so that it may use differentchannel structures according to the presence or absence of data in thetransmitted control signal.

FIG. 3 is a structural diagram illustrating a channel structure for usein a specific case in which only a control signal excepting data istransmitted.

The exemplary case of FIG. 3 shows that the control signal has no datato be transmitted. As can be seen from FIG. 3, some areas of a systembandwidth are classified according to a frequency division multiplexing(FDM) scheme, and a control signal is allocated to the divided areas.Specifically, a control-channel area allocated for transmission of thecontrol signal without transmitting data may be located at both ends ofthe system bandwidth as shown in FIG. 3.

A user equipment (UE) capable of transmitting only the control signalusing the above-mentioned control channel may demodulate the controlsignal in the allocated area according to the SC_FDM scheme, and maytransmit the demodulated control signal to the allocated area. Accordingto a scheme for transmitting the control signal in the above-mentionedallocated area, a FDM or code division multiplexing (CDM) scheme may beapplied to UE control signals within the allocated area.

FIG. 4 is a structural diagram illustrating a channel structure for usein a specific case in which data and a control signal are simultaneouslytransmitted.

If the data and the control signal are simultaneously transmitted, someareas of the system bandwidth are classified according to the FDMscheme, and may then be allocated to transmit a control channel. In thiscase, the transmission scheme is not considered to be the SC-FDM scheme,and corresponds to a multi-carrier transmission scheme. Therefore, inthe case of simultaneously transmitting the data and the control signal,the present invention transmits both the data and the control signalusing the DFT spreading scheme, so that the SC-FDM scheme is maintainedand the PAPR of the transmission signal is reduced. In this case, amethod for adding the data and the control signal may be a time divisionmultiplexing (TDM), CDM, or modulation-based transmission scheme. FIG. 4shows that the control signal and the data are transmitted according tothe TDM scheme.

If there is no control signal in the structure of FIG. 4, a method forincreasing a coverage can be implemented. If there is a need to stronglytransmit a control signal, a specific control signal is repeatedlyinserted into each OFDM symbol, so that the power of the control signalcan be increased by about 10*log 10(12)=10.8 dB.

In association with the above-mentioned control channel structure, thefollowing description relates to a specific case in which the TTI-unitsymbol modulated in time and frequency directions is applied to acontrol channel for transmitting only the control signal and excludingother data. In other words, the following description relates to acontrol signal transmission structure capable of transmitting morecontrol information without affecting the PAPR/CM of a control signal inthe basic control channel structure shown in FIG. 3.

However, a method for generating the TTI-unit symbol and transmitting asignal according to each embodiment of the present is not limited toonly the above-mentioned transmission of the control signal, and canalso be applied to a predetermined system which uses a TTI as atransmission unit.

In the case of implementing the above-mentioned embodiment using achannel capable of transmitting only the control signal and excludingother data, a CAZAC sequence can be generally used as a sequence fortransmitting the control signal. In more detail, a Zadoff-Chu (ZC) CAZACsequence can be used as the sequence for transmitting the controlsignal.

The above-mentioned CAZAC sequence will hereinafter be described.

The CAZAC sequence is generally classified into the Zadoff-Chu (ZC)CAZAC sequence and a GCL CAZAC sequence. The relationship between theZadoff-Chu (ZC) CAZAC sequence and the GCL CAZAC sequence is representedby a conjugate complex number. In more detail, the GCL CAZAC sequencecan be acquired by a conjugate complex number of the Zadoff-Chu (ZC)CAZAC sequence.

The Zadoff-Chu (ZC) CAZAC sequence can be represented by the followingequations 1 and 2:

$\begin{matrix}{{{c\left( {{k;N},M} \right)} = {\exp \left( \frac{{j\pi}\; {{Mk}\left( {k + 1} \right)}}{N} \right)}}\left( {{for}\mspace{14mu} {odd}\mspace{14mu} N} \right)} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\{{{c\left( {{k;N},M} \right)} = {\exp \left( \frac{{j\pi}\; {Mk}^{2}}{N} \right)}}\left( {{for}\mspace{14mu} {even}\mspace{14mu} N} \right)} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

wherein “k” is a sequence index, “N” is the length of a CAZAC sequenceto be generated, and “M” is a sequence ID.

If the length (N) of the above-mentioned ZC sequence is represented by aprime number, the largest number of sequences can be used. If thesequence length (N) is not represented by the prime number, the ZCsequence is effective in the N value and a relative prime number “M”(where M=1˜N−1). Therefore, it is preferable that the length of asequence to be used is represented by the prime number.

In the case of transmitting the control signal without transmitting dataaccording to the 3GPP LTE, a control channel can be designed as shown inFIG. 3. A basic allocation unit is called a resource block (RB). Thisresource block (RB) includes 12 sub-carriers.

If the value of the basic allocation unit is not represented by theprime number, it is preferable that a sequence having a prime-numberlength may be generated according to the length of the basic allocationunit.

There are proposed a variety of methods for generating theabove-mentioned sequence having the prime-number length, for example, afirst method for generating a sequence having a prime-number lengthlonger than the N value, and cutting the sequence by a predeterminedlength (N) to be used; and a second method for generating a sequencehaving a prime-number length shorter than the N value, and disregardingthe remaining parts or filling the remaining parts with “0”. Also, afirst method may be proposed. According to this third method, if the Nlength is not represented by the prime number, the CAZAC sequence mayhave the above-mentioned N length without any change. Theabove-mentioned third method has very few sequences. In this way, in thecase of directly generating the sequence using the sequence length to beused, the generated sequence has superior correlation characteristicsbetween sequences or the signal uniformity (e.g., PAPR or cubic metric)in time and frequency domains.

The following description of the present invention assumes that theabove-mentioned first, second, and third methods can be used, so thatone of them is properly selected according to an appropriate RB size andthe number of symbols used in a TTI.

In order to transmit information using the CAZAC sequence, two methodscan be used. A first method uses a CAZAC index to transmit informationvia the CAZAC sequence. A second method applies a cyclic shift (alsocalled a circular shift) to a sequence corresponding to each CAZAC indexin order to indicate desired information.

The second method includes a first case for directly cyclic-shifting theCAZAC sequence and a second case for applying the cyclic shift using adomain conversion. For example, according to the domain conversion, anexponential function is multiplied in a frequency domain so that atime-domain cyclic shift is applied to the frequency domain, or anexponential function is multiplied in a time domain so that afrequency-domain cyclic shift is applied to the time domain.

Based on the above-mentioned description, a direction modulation schemeand a sequence modulation scheme will hereinafter be described asdetailed examples of the above-mentioned embodiment shown in FIG. 2.

The direct modulation scheme performs the DFT spreading on atransmission signal and then performs an OFDM modulation on the spreadresultant signal.

In other words, the direct modulation scheme performs the spreadingprocess using the DFT spreading module 101 of FIG. 1, modulates afrequency-direction modulation and an additional time-directionmodulation according to the above-mentioned embodiment of the presentinvention, and generates a TTI-unit symbol by the IFFT module 102.

The sequence modulation scheme loads a specific sequence (e.g., CAZAC,Walsh, Hadamad, Golay, or PN) to a sub-carrier. In other words, asequence used in the sequence modulation scheme is used as information.The cyclic shift may be additionally applied to a specific sequence.

Detailed examples of the above-mentioned schemes will hereinafter bedescribed.

FIG. 5 is a conceptual diagram illustrating a method for generating aTTI-unit symbol modulated in time and frequency directions according toa sequence modulation scheme.

As shown in FIG. 5, a specific transmission sequence (e.g., CAZAC,Walsh, Hadamad, Golay, or PN) may be loaded on each sub-carrier, so thatthe resultant sub-carrier including the specific transmission sequencemay be transmitted.

In this case, a sequence loaded on each sub-carrier is shown in FIG. 5.In FIG. 5, the above-mentioned specific transmission sequence (s0˜s13)(e.g., CAZAC, Walsh, Hadamad, Golay, or PN) may be multiplied by atime-domain modulation sequence (x0˜x13) having a predetermined lengthdenoted by the 1 TTI.

In more detail, the specific sequence (s(0)x(0)˜s(13)x(13)) modulated inthe time domain may be mapped to each sub-carrier, so that the mappingresult may be transmitted.

In the meantime, if required, the above-mentioned time-domain modulationsequence (s(0)x(0)˜s(13)x(13)) mapped to each sub-carrier may bemultiplied by a frequency-domain modulation sequence (c(k)). In thiscase, the frequency-domain modulation sequence c(k) may be representedby an exponential function, so that a transmission sequence s(n) can becyclic-shifted in the time domain by the exponential function shown inthe following equation 3:

c(k)=exp(−jSw ₀ k)  [Equation 3]

In Equation 3, “n” is a time-domain symbol index, “k” is afrequency-domain sub-carrier index, “ ” is a unit phase associated witha cyclic shift, and “S” is an indeed value indicating the degree of thecyclic shift.

Therefore, transmission information in the finaltime/frequency-domain-modulated TTI unit sequence can be classified intoa cyclic shift of c(k), a transmission sequence of s(n), and cyclicshift information of x(n).

In the case of generating/transmitting the TTI unit symbol according tothe above-mentioned scheme, there is no distortion in the PAPR/CM, sothat more transmission information can be transmitted. In the meantime,the use of the s(n) value may be changed according to the amount of datato be transmitted. In other words, in the case of s(n), the same valuemay be assigned to all of “n” values (wherein transmission informationis transmitted to the remaining two options), or different values mayalso be assigned to the “n” values.

In the meantime, according to a detailed embodiment of the presentinvention, the Frequency Hopping is additionally applied to the TTI unitsymbol generated by the sequence modulation scheme of FIG. 5, so that anadditional diversity gain can be acquired.

FIGS. 6 and 7 are conceptual diagrams illustrating a variety of methodsfor applying the hopping to the TTI-unit symbol of FIG. 5 according tothe present invention.

Referring to FIGS. 6 and 7, if the TTI unit symbol generated by thescheme of FIG. 5 is applied to a control channel structure capable oftransmitting only a control signal and excluding other data, i.e., if acontrol signal is transmitted over a sub-carrier area acting as acontrol channel, which has been allocated to one end or both ends of asystem band, the transmission structure of FIG. 6 or 7 changes atransmission frequency band in units of a predetermined symbol so thatit acquires a frequency-domain diversity gain.

The reason why the hopping scheme is applied to the structure of FIG. 6or 7 is to acquire a diversity gain along a propagation path althoughone channel has a poor condition.

In more detail, FIG. 6 shows an exemplary structure in which a frequencyband of each symbol is changed at intervals of a predetermined timecorresponding to a single symbol. FIG. 7 shows an exemplary structure inwhich the 1 TTI is divided into two sections, so that symbols of eachdomain are transmitted over different frequency bands.

The hatching parts of FIG. 6 or 7 indicates a location at which controlinformation is transmitted, and the non-hatching parts of FIG. 6 or 7indicates a location at which the control information is nottransmitted. It should be noted that symbols generated by differentsequences may be transmitted to the hatching and non-hatching parts ofFIG. 6 or 7, or different parts of symbols generated by the samesequence may also be transmitted to the hatching and non-hatching parts.

FIG. 8 is a conceptual diagram illustrating a method for generating theTTI-unit symbol modulated in time and frequency directions according toa direct modulation scheme according to another embodiment of thepresent invention.

Referring to FIG. 8, the direct modulation scheme directly loads atransmission sequence on a sub-carrier, differently from the sequencemodulation scheme of FIG. 5. In this way, in the case of generating asignal according to the direct modulation scheme, the generated signalmust undergo the spreading caused by the DFT module 101, and a sequenceused as a mask in a sub-carrier level is used according to a spectralshaping scheme.

In this case, if a transmission sequence s(k) loaded on the sub-carrierhas the same value for each OFDM symbol, additional information (e.g.,cyclic shift) may be acquired from the frequency-direction modulationsequence c(k) used as a sub-carrier-directional masking.

Differently from the above-mentioned description, if different symbolsare applied to sub-carriers of all the OFDM symbols, thefrequency-direction modulation sequence c(k) may be set to a scramblingsequence.

In the meantime, the frequency-domain-modulated sequences may beadditionally modulated in a time domain by the time domain modulationsequences x(0)˜x(13) in the TTI unit as shown in FIG. 8.

Therefore, in the time/frequency-direction modulated TTI-unit symbolss(k) shown in FIG. 8, transmission information may also be transmittedvia each sub-carrier symbol s(k), a sub-carrier level-modulationsequence c(k), or a TTI-unit time-domain modulation sequence x(n).

The hopping scheme of FIG. 6 or 7 can also be applied to theabove-mentioned direct modulation scheme. However, each sub-carrierlevel of the direct modulation scheme requires accurate channelestimation due to a sub-carrier level modulation of the transmissionsequence, so that it is preferable that the hopping may not be appliedto the direct modulation scheme or may also be applied to the sameaccording to the scheme of FIG. 7.

In the meantime, in association with FIGS. 5 to 8, the transmissionsequence s(k) disclosed in the above-mentioned TTI-unit symbolgeneration method may indicate specific control information to betransmitted.

In this case, the above-mentioned control information may indicateeither one of control information (e.g., ACK/NACK, or CQI). However, itshould be noted that heterogeneous control information (e.g., ACK/NACK,and CQI) may be scrambled by the DFT spreading. In other words, oneembodiment of the present invention may scramble heterogeneous controlinformation at a position ahead of the DFT spreading module of FIG. 1,so that a transmission sequence may be generated according to thescrambled result.

A method for transmitting a TTI-unit signal according to anotherembodiment of the present invention will hereinafter be described.

FIG. 9 is a flow chart illustrating a method for transmitting a TTI-unitsymbol according to the present invention.

The TTI-unit signal transmission method considers that a communicationsystem simultaneously transmits signals in TTI units, instead of symbolunits, so that each transmission sequence is masked in a time-domainsymbol within the 1 TTI and the masking result is transmitted. In thiscase, the transmission sequence may be a time-direction sequence persub-carrier of a time/frequency-direction-modulated TTI unit symbol.Otherwise, the transmission sequence may be a predetermined symbol unittransmission sequence in the same manner as in the above-mentionedembodiment.

The above-mentioned predetermined symbol unit sequence or thetime-direction sequence per sub-carrier of the TTI unit symbol aremasked in each OFDM symbol area associated with the time domain withinthe 1 TTI at step S901. For the convenience of description, thepredetermined symbol unit sequence and the time-direction sequence aregenerically named “input sequences”.

In this case, the input sequences may be sequentially masked in eachOFDM symbol. If the cyclic shift is applied to the order of masking theinput sequences in the OFDM symbol, additional information may also betransmitted. The above-mentioned cyclic shift is indicative of asymbol-unit cyclic shift, and is different from those of FIGS. 5 to 8.As previously stated above, the cyclic shift of FIGS. 5 to 8 has beendesigned to be applied within each symbol.

Thereafter, the time-domain-modulated sequence generated at step S901 istransmitted in TTI units at step S902. According to this method, thetransmission sequence is modulated in a time direction so thatadditional information can be transmitted.

If the above-mentioned scheme is applied to a control channel structurefor transmitting only the control signal and excluding other data in theSC-FDM-based communication system, a detailed description thereof willhereinafter be described.

FIG. 10 is a conceptual diagram illustrating a method for performing atime-domain modulation on a transmission symbol in TTI units, andtransmitting the modulated symbol according to one embodiment of thepresent invention.

In more detail, the exemplary structure of FIG. 10 is acquired when aCAZAC sequence acting as a transmission symbol is applied in a timedomain of a TTI unit. The structure of FIG. 10 is acquired when theCAZAC sequence is modulated in a predetermined resource block (which isconsidered to be a single lump irrespective of signal structures) ofeach OFDM symbol.

If the OFDM symbol structure is considered in the 3GPP LTE, a total of14 OFDM symbols are contained in the 1 TTI, so that the CAZAC sequencemay have the length denoted by N=14. In this case, there are a varietyof methods for generating transmission sequences respectively mapped tothe OFDM symbols in a time domain, for example, a cyclic copy scheme forgenerating/using a sequence based on a prime-number length to guaranteea sufficient number of CAZAC sequences, a truncation scheme, and amethod for employing the length of N=14 without any change. Inassociation with FIG. 2, as described above, the present invention mayuse sequences, per sub-carrier, of TTI unit symbols modulated in thetime and frequency directions.

If the transmission sequences are masked in the time-domain OFDM symbol,a cyclic shift toward the time domain may be applied to the transmissionsequences as shown in FIG. 10.

In more detail, transmission sequences are sequentially masked in firstand second sub-carriers of FIG. 10. However, at a third sub-carrier, thecyclic shift corresponding to two OFDM symbols is applied totransmission sequences of the third sub-carrier, so that thecyclic-shifted sequences are transmitted. At a fourth sub-carrier, thecyclic shift corresponding to seven OFDM symbols is applied totransmission sequences of the fourth sub-carrier. The above-mentionedtime-direction cyclic shift within the TTI is performed in symbol unitswhen transmission sequences are mapped to the OFDM symbols, and isdifferent from those of FIGS. 5 to 8 in which the cyclic shift has beenapplied within a single OFDM symbol.

Therefore, in the case of masking the CAZAC sequence in symbol units,the present invention may acquire the sufficient number of cyclic shiftsavailable for the CAZAC sequence, wherein the number of cyclic shiftscorresponds to a sequence length. This cyclic shift of FIG. 10 canmaintain orthogonality between sequences even when the delay spreadingis very large, differently from the cyclic shifts of FIGS. 5 to 8.

Also, the cyclic shift of FIG. 10 uses a sequence having 14 lengthscorresponding to the number of symbols contained in the TTI, so that thenumber of applicable cyclic shifts may also be set to “14”. The numberof root sequences varying with the length is set to about “14”, so thatthe embodiment of FIG. 10 can guarantee many more root sequences thanthose of another case in which the length of 12 sub-carriers is used ina frequency domain, thereby solving the cell planning problem.

And, the transmission scheme of FIG. 10 applies a symbol-unit cyclicshift within the TTI to TTI unit symbols generated by the schemes ofFIGS. 5 to 8, so that it can transmit additional information.

According to the embodiment of FIG. 10, UEs can be distinguished fromeach other by the cyclic shift or the root sequence index. Oneembodiment of the present invention provides a method for using thecyclic shift of FIG. 10 to make a UE distinction or using the samecyclic shift as control signal information.

For example, the scheme of FIG. 10 allocates two cyclic shift sequenceshaving the same root sequence indexes to a single UE, and allowsACK/NACK values to correspond to individual cyclic shift values, so thatthe resultant signal is transmitted. This format can be effectively usedwhen the ACK/NACK channels are constructed in a control channel of FIG.3 according to the FDM scheme.

According to a coherent scheme, the use of the CAZAC sequence is limitedin the FDM scheme, a pilot is required for transmitting a messagebecause a control symbol is directly applied to each sub-carrier.

According to a non-coherent scheme, the CAZAC sequence is masked in thetime domain as shown in FIG. 10 and different cyclic-shift sequences aredirectly applied to the masked result according to the controlinformation, so that 7 ACK/NACK signals per FDM resource block can besimultaneously transmitted.

According to one embodiment of the present invention, the presentinvention transmits control information using the symbol-unit cyclicshift in the time domain, so that it discriminates between a variety ofinformation using the cyclic shift itself without using the pilot, andtransmits the resultant information. As a result, the present inventioncan support a non-coherent searching scheme of a reception end.

According to another embodiment of the present invention, the presentinvention may further support the coherent detection scheme, which usesa time-domain symbol-unit cyclic shift to additionally discriminatebetween users or UEs and makes a distinction of control information bychannel estimation based on the pilot.

A method for supporting the coherent scheme and the non-coherent schemewill hereinafter be described in detail.

According to a detailed embodiment of the present invention, thefrequency hopping for acquiring the diversity gain may be additionallyapplied to the transmission method of FIG. 10.

FIGS. 11 to 14 are conceptual diagrams illustrating a variety of methodsfor applying the hopping to a transmission format shown in FIG. 11according to the present invention.

Referring to FIGS. 11 to 14, if the CAZAC sequence is used as atransmission sequence of a time-direction symbol unit as shown in FIG.10, and the channel hopping is performed to acquire a diversity gain ona frequency axis, the hopping of sequence modulation also occurs. InFIGS. 11 to 15, the same background patterns are indicative of the sametransmission sequences.

In this case, two access methods can be considered. According to a firstmethod, as shown in FIGS. 11 and 12, a sequence having the length of 14is masked in a resource area without any change irrespective of thefrequency hopping, after the resource area has been frequency-hopped atintervals of a predetermined symbol, so that the first method has anadvantage in that it can maintain the sequence length of 14.

In the meantime, due to the aforementioned hopping, channel responsesassociated with channel resources (i.e., control channel resources) maybe different from each other. These different channel resources mayunexpectedly affect the orthogonality of sequences, so that anotherembodiment of the present invention provides a method for applying thesame sequences to only OFDM symbols contained in the same resource, asshown in FIGS. 13 and 14.

If the same sub-carrier is repeatedly used by the hopping of acontrol-signal location as shown in FIGS. 13 and 14, a sequence lengthcorresponding to the number of repeating times of the sub-carrier isadapted to perform the masking. In this case, the length of atransmission sequence of FIG. 13 or 14 is the half of that of FIG. 11 or12.

In the meantime, according to a detailed embodiment of the presentinvention, although there is no hopping process as shown in FIG. 10, thepresent invention may also perform a modulation process using ahalf-length CAZAC sequence, so that it can be compatible with theabove-mentioned case of FIG. 13 or 14 in which the sequence length iscut in half by the frequency hopping.

The above-mentioned embodiment of the present invention has disclosedthe method for supporting the non-coherent searching scheme capable ofdiscriminating between different control information using only thecyclic shift applied to the sequence. In the case of supporting thenon-coherent searching scheme, the amount of transmittable informationin the non-coherent searching scheme may be less than that of thecoherent searching scheme.

Therefore, one embodiment of the present invention provides a method forinserting a pilot in a control channel to search for control informationaccording to the coherent scheme, simultaneously while considering thenumber of guaranteed sequences and the accuracy of channel estimation.

In more detail, in the case of using the same sequence as the CAZACsequence, it is more preferable that the length of the sequence has aprime number in order to guarantee a sufficient number of sequences. Forexample, if the above-mentioned process is performed in 14 OFDM symbolunits, the pilot is inserted into a single OFDM symbol, so that thesymbol length to which the sequence is applied may be set to “13”. And,under the same situation, the pilot is inserted into three OFDM symbols,so that the symbol length to which the sequence is applied may be set to“11”.

FIGS. 15 to 17 are conceptual diagrams illustrating method for insertinga pilot into a TTI-unit symbol based on the coherent scheme according toone embodiment of the present invention.

In the case of inserting the pilot into a single OFDM symbol as shown inFIG. 15, it is preferable that the frequency hopping is not in use. TheOFDM symbol in which the pilot is inserted may be located at the centerof a transmission unit, so that the channel estimation can beeffectively performed at the center of the transmission unit.

FIG. 15 shows an exemplary structure in which the pilot is applied to aseventh or eighth OFDM symbol from among 14 OFDM symbols of the 1 TTI.

FIG. 16 shows an exemplary structure in which the pilot is applied tothree OFDM symbols from among 14 OFDM symbols of the 1 TTI, and thefrequency hopping is applied to seven OFDM symbols from among the 14OFDM symbols.

As can be seen from FIG. 16, three OFDM symbols are used for pilots. Inthe case of applying the frequency hopping the structure of FIG. 16, asingle OFDM symbol for only one pilot is arranged at one of two parts(each part composed of 7 OFDM symbols), and two OFDM symbols for twopilots are arranged at the other one. The single OFDM symbol for onlyone pilot is arranged at the center of a corresponding hopping area, andthe remaining two OFDM symbols for two pilots are spaced apart from eachother by a predetermined distance in the other hopping area.

FIG. 17 shows an exemplary structure in which three OFDM symbols fromamong 14 OFDM symbols within the 1 TTI are used for pilots, and thefrequency hopping is not applied to the structure of FIG. 17. In thisway, if three OFDM symbols are used as pilots without performing thefrequency hopping, it is preferable that these three OFDM symbols may beequally arranged at the center part within the 1 TTI.

According to this embodiment employing the coherent searching scheme, ifpilots are arranged as shown in FIGS. 15 to 17, the length of amodulated sequence may be denoted by a prime number. So, in the case ofusing the CAZAC sequence, the above-mentioned embodiment based on thecoherent searching scheme can acquire a maximum number of sequences,OFDM symbols for pilots are spaced apart from each other by the samedistance in the center part of a transmission area, so that it canimprove a channel estimation performance.

In the meantime, if the number of OFDM symbols to be used as pilots ischanged, for example, if two pilots (or three pilots) are allocated toeach hopping area of FIG. 16, the sequence length in each hopping areais 10 (or 8), so that the sequence length to be used is not denoted by aprime number.

In this case, basically, the pilots are spaced apart from each other bythe same distance in the hopping area, so that they provide other OFDMsymbols with an appropriate channel estimation performance. However, itshould be noted that the above-mentioned pilots may also be arranged toshare a pilot location of a data area.

According to one embodiment of the present invention, if the number ofOFDM symbols to be applied to a sequence is not denoted by a primenumber, the present invention generates the sequence on the basis of thelength of a prime number less than the number of OFDM symbols, andperforms the cyclic copy on the remaining parts or inserts the value of“0” in the same remaining parts, so that it can guarantee a maximumnumber of sequences of a corresponding OFDM symbol length. Also, thepresent invention generates a sequence on the basis of the length of aprime number higher than the number of OFDM symbols, truncates asequence part longer than the number of OFDM symbols, and guarantees thenumber of available sequences.

The above-mentioned description has disclosed the method fortransmitting a control signal to support the coherent searching schemeand method for transmitting such a control signal to support thenon-coherent searching scheme. In the meantime, according to oneembodiment of the present invention, the coherent searching scheme maybe combined with the non-coherent searching scheme, and a detaileddescription thereof will hereinafter be described.

FIGS. 18 and 19 are conceptual diagrams illustrating methods for merginga coherent-based channel with a non-coherent-based channel, and usingthe merged result according to embodiments of the present invention.

The embodiment of FIG. 18 or 19 properly combines the coherent schemewith the non-coherent scheme, so that there is no need to insert thepilot in the coherent scheme, and the number of transmittableinformation is not reduced in the non-coherent scheme.

Specifically, one half of a control channel has a signal structure forthe coherent searching, i.e., a control signal symbol directly indicateseach symbol. The other half uses a signal structure for the non-coherentsearching, wherein each symbol does not indicate a control signalsymbol, and each sub-carrier area is designed to indicate a signal usingeither the sequence itself or the cyclic shift applied to this sequence.

Referring to FIGS. 18 and 19, as can be seen from an upper left part andlower right part inside of the TTI, pilots are inserted into the upperleft part and the lower right part to perform the coherent searching,and are then transmitted.

A lower left part and an upper right part in the TTI in FIGS. 18 and 19indicate corresponding information using the sequence itself or thecyclic shift applied to this sequence, resulting in the implementationof the non-coherent searching.

Needless to say, the coherent area and the non-coherent area of FIGS. 18and 19 may be replaced with each other, and the number of symbols forpilots in the coherent area may also be different from that of FIG. 18or 19 as necessary.

As described above, the method for generating the TTI-unit OFDM symboland transmitting the TTI unit according to various embodiments of thepresent invention can be applied to a variety of situations, and it cansupport both the coherent scheme and the non-coherent scheme.

Individual embodiments of the present invention can be applied to thecommunication system according to a variety of schemes, for example, acoherent scheme, a non-coherent scheme, and a combination thereof, anddetailed description thereof will hereinafter be described in detail.

The coherent transmission/reception scheme must perform channelestimation at a reception end, and must perform a channel operation forcompensating for the channel estimation at the reception end, so thatpilot signals must be inserted as shown in FIGS. 15 to 17. If the pilotsignals are inserted into the structures of FIGS. 15 to 17, the numberof OFDM symbols available for the transmission sequences in the timedomain is reduced.

For example, if 14 OFDM symbols exist in a single sub-frame (i.e., 1TTI) based on the 3GPP LTE (i.e., if a short cyclic prefix (CP) isused), and a control-channel pilot is determined to have the samestructure as that of a data part in the 14 OFDM symbols (i.e., if twosymbols are used as pilots), 12 OFDM symbols can be used as transmissionsequences.

Therefore, the time-domain scrambling or spreading sequence x(n) of FIG.5 or 8 is set to “12” if the hopping is not applied to the sequencelength. Otherwise, if different sub-carrier areas use differentsequences by the hopping, the value of x(n) is reduced to “6”. Ifreference symbols are additionally used, the length of asequence-transmission symbol is reduced by a predetermined lengthcorresponding to the number of the reference symbols.

In order to generate the TTI unit symbol according to the embodiment ofFIG. 5 or 8, the spreading or scrambling sequence “c(k)” (See FIG. 5 or9) is applied to the above-mentioned time-domain sequence includingpilots. In this case, the sequence “c(k)” is spread or scrambled on atime axis.

If a control signal to be transmitted has a small amount of signal ofabout one or two bits (e.g., ACK/NACK signal), a transmission sequence“s(k)” is fixed at a frequency axis, a sequence multiplied by all theparts of a single OFDM symbol is BPSK- or QPSK-modulated, so that theresultant sequence may indicate the ACK/NACK, as shown in FIG. 5.

In order to transmit more information (e.g., CQI, and PMI), thefollowing two methods can be used.

Firstly, as shown in FIG. 5, less number of bits from among control datais QAM-marked and is multiplied in all parts of a single control OFDMsymbol, and additional bits may be applied to other control OFDMsymbols. Otherwise, control data is directly QAM-modulated on afrequency axis, and the resultant data may be applied to sub-carriers.In this case, the sequence “c(k)” performs the scrambling, or may be aUE specific (i.e., a specific UE) or a cell/node-B specific sequence.

If the hopping is also applied to the above-mentioned case, sequencesused in a single slot (i.e., the half of a single sub-frame) may beestablished differently from those of the remaining slots. In the caseof applying the MIMO diversity, the diversity can be applied to thefrequency axis and the time axis. In the case of applying the MIMOdiversity to the frequency axis, a Space-Frequency Block Coding (SFBC)scheme is applied to the structure of FIG. 8. If the case of applyingthe MIMO diversity to the time axis, the SFBC scheme may be applied tothe structure of FIG. 5. In other words, the block coding may be appliedto different transmission sequence locations, so that the block-codingresult may be transmitted.

Next, in the case of supporting the non-coherent transmission/receptionscheme, a reception end has no need to perform channel estimation, sothat additional transmission pilots are not required. However, apreferred embodiment of the present invention considers a collision witha data part, and then provides a method for controlling the OFDM symbolpart including the pilots not to be used to transmit a control signal.In this case, as previously stated in the above-mentioned coherentscheme, the time-domain modulation sequence x(n) is reduced by thenumber of OFDM symbols used for pilot transmission.

In the case of supporting the non-coherent transmission/receptionscheme, channel estimation is no longer required so that a method fortransmitting a control signal can be classified into an implicitmodulation scheme and an explicit modulation scheme.

The implicit modulation method does not transmit a direct controlsignal, and makes a distinction of the control signal using a sequencecombination or index.

The explicit modulation scheme directly transmits a control signal tothe sequence, so that it can perform the channel estimation. As aresult, it is preferable that a differential modulation scheme may beused as a modulation scheme.

The implicit modulation scheme and the explicit modulation scheme willhereinafter be described in detail.

Firstly, the implicit modulation scheme is advantages to transmit asmall amount of information. In other words, a transmission sequences(k) or s(n) is generally set to “1”, and information is generated bycombination of a frequency-direction modulation sequence c(k) and atime-direction modulation sequence x(n).

In more detail, if a specific sequence is transmitted on the conditionthat a predetermined set from among available sequences has been fixed,a reception end performs the mapping of sequence set informationcorresponding to the control signal, and searches for desiredinformation. In association with the predetermined set, a single UE usesa single sequence (on-off keying) or two sequences (sequence-keying) forone bit.

In this way, only one of “c(k)” and “x(n)” may be selected when thesequence set is configured, and the combination of them “c(k)” and“x(n)” is considered to be a single new sequence so that the combinationresult may be mapped to a control signal.

For example, if the number of available sequences c(k) is set to “12”,and the number of available sequences x(n) is set to “7”, a total of 84sequence combinations (i.e., 12*7) can be used. And, if the slot-unithopping is performed, sequences at the hopped positions may constructother combinations (i.e., one of the sequences c(k) and x(n), or thecombination of the sequences c(k) and x(n)). In other words, if a singleUE performs the on-off keying in a single slot, it can extract bitinformation stored in a first slot and the other bit information storedin a second slot in different ways. Also, one UE may combine sequencetransmission information of one slot with those of the other slot, andmay detect a signal according to the combined result. For example, inthe case of using two sequence combinations A and B, a signal can betransmitted according to four combinations [A,A], [A,B], [B,A], and{B,B]. Therefore, a receiver may detect the above-mentioned twocombinations in two slots, convert the detected combinations into aspecific bit combination, and analyze the converted result.

The explicit modulation scheme will hereinafter be described in detail.In the case of transmitting a control signal as modulation information,there is needed a method for detecting a data symbol without performingthe channel estimation as in the above-mentioned differentialmodulation, so that the explicit modulation scheme can receive thecontrol signal using the non-coherent scheme.

There are two kinds of differential modulation methods, i.e., a firstdifferential modulation method and a second differential modulationmethod. The first differential modulation method uses a change of amodulation value (generally a phase difference) between neighboringsub-carriers on a frequency axis as single control signal information.The second differential modulation method uses a change of a modulationvalue between different OFDM symbols on a time axis as control signalinformation.

In order to transmit much more information, a two-dimensional (2D)differential modulation scheme can be considered. The 2D differentialmodulation scheme may perform a differential encoding process for eachOFDM symbol on a frequency axis, or may allow each sub-carrier to havedifferential modulation information among different OFDM symbols on atime axis.

The diversity scheme may also be applied to the non-coherent scheme, sothat the Space-Frequency Block Coding (SFBC) or the Space-Time BlockCoding (STBC) is applied to a frequency axis or a time axis in the samemanner as in the coherent scheme, thus generating a control signal.

Next, a method for combining the coherent scheme with the non-coherentscheme according to one embodiment of the present invention willhereinafter be described.

A control channel structure (e.g., ACK/NACK channel structure) and atransmission/reception technique of the coherent scheme are differentfrom those of the non-coherent scheme according to transmissioncapability, UE capability, and channel characteristics. In more detail,the coherent scheme supports transmission of a small amount ofinformation composed of one or two bits by converting a modulationtechnique into another method, so that its UE capability is superior tothat of the non-coherent scheme.

However, the coherent scheme is greatly dependent on the channelestimation, so that its channel estimation reliability is lowered inhighly-time-varying mobile environments. As a result, the coherentscheme has difficulty in maintaining orthogonality, resulting indeterioration of its performance.

The non-coherent scheme based on the implicit modulation requiresallocation of additional sequences whenever each 1-bit transmission isadded, so that its UE capability required for transmitting informationcomposed of at least 2 bits is lowered. Needless to say, if thenon-coherent scheme discards a slot-unit frequency hopping gain so as tosolve the above-mentioned problem, the non-coherent scheme can maintaindesired UE capability. However, it should be noted that a diversity gainof the non-coherent scheme is lowered, resulting in the occurrence ofperformance deterioration. Although a channel variation is relativelylarge as in a high-speed mobile environment, the non-coherent scheme issuperior to the coherent scheme highly dependent on channel estimation.

In this way, in order to maximize the efficiency of transmission of asmall amount of control signal, the coherent scheme or the non-coherentscheme can be selectively determined, so that a control channel requiredfor the selected scheme is also required.

According to the present invention, it is assumed that a resourcestructure for a basic control channel considers the slot-unit hoppingshown in FIG. 16, the number of reference signals for each slot is notfixed, and the resource structure is constructed using one RB (i.e., 1RB) as a basic unit. And, it is assumed that a sequence length of afrequency domain is 12, the resource structure uses 6 sequences byperforming the cyclic shift on a CAZAC of a specific index, and thespreading code of a time domain uses a maximum length “7” on the basisof a slot. Needless to say, the present invention may configure avariety of combinations as necessary, for example, a spreading code withthe length of 3 and a spreading code with the length of 4 may beconfigured.

In conclusion, according to the above-mentioned embodiment, the presentinvention can generate a total of 42 orthogonal channels (i.e., 42=7*6)in one slot, and the coherent or non-coherent scheme requires twoorthogonal channels or orthogonal codes to transmit information of 1bit. 42 codes are grouped into 21 pairs of codes (i.e., 21 code-pairs),these 21 code-pairs are allocated to a UE, and the UE uses the 21code-pairs, so that the scrambling structure of the coherent andnon-coherent schemes can be easily supported.

As previously stated above, the present invention may configure avariety of combinations by division of the time-domain spreading code,so that it can establish a variety of code-pair structures according tochannel characteristics and UE capability.

In the meantime, as described above, according to another embodiment,the present invention provides a transmission signal generation methodcapable of supporting a multi-format or acquiring a variety of spreadinggains.

According to the above-mentioned method for generating thetransmission-unit symbol in time and frequency domains, the presentinvention can transmit additional information by modulating transmissioninformation in time and/or frequency directions. Also, the presentinvention generates a transmission signal by modulation of time andfrequency domains, so that it can be applied to a transmission signalgeneration method capable of supporting a variety of control signalformats.

In the case of generating a control signal using the schemes of FIGS. 5and 8, if a UE must transmit a control signal (e.g., ACK/NACK signal)using only a predetermined number of bits, the present inventionnon-coherently detects a corresponding sequence using a sequencecombination, uses a predetermined number of symbols from among severaltransmission signals as a pilot (wherein the number of OFDM symbols tobe used as actual pilots must be optimized), and directly corrects aphase of a data symbol.

However, if the number of bits of transmission information is changed inthe control channels of FIGS. 5 and 8, flexibility or adaptability maybe decreased.

In other words, provided that a maximum number of bits capable of beingtransmitted within a specific error rate are “10” (i.e., 10 bits) on thecondition that a single resource block is configured as a control signalchannel, another channel structure must be designed to transmit morebits. However, an unexpected interference may occur between neighboringcells employing different channel structures. In order to remove theinterference, the neighboring cells must use the same channel structure.Therefore, although another channel structure is designed, theinterference cannot be solved. Therefore, there must be designed animproved structure, which reduces the interference between neighboringcells simultaneously while transmitting a variable amount ofinformation.

Therefore, the present invention provides a transmission signalgeneration method. The transmission signal generation method maintainsthe PAPR/CM characteristics of a control signal during the transmissionof the control signal, allows each UE to support a variety of controlsignal formats, and has no problem in a multi-cell operation.

FIG. 20 is a conceptual diagram illustrating a method for spreading aninformation symbol in symbol units in a frequency domain, performing amodulation process in each domain by multiplexing atime/frequency-domain modulation/masking sequence, and transmitting atransmission (Tx) signal according to the modulated result.

Differently from the methods of FIGS. 5 and 8, the method of FIG. 20 isable to generate a signal capable of being transmitted to acorresponding channel, although the length of the spreading ormodulation/masking sequence is set to a total length available in acorresponding channel or is shorter than the total length available inthe corresponding channel.

In more detail, the methods of FIGS. 5 and 8 use a sequence capable ofusing all parts of a maximum length available in a given area of acorresponding channel. In this case, the transmitted control signalshave the same robustness (e.g., BER or FER). However, the ACK/NACKsignal from among actual control signals requires a very low BER asdescribed above whereas a relatively high BER is allowed in the CQI/PMIinformation.

In the case of considering the above-mentioned case, the above-mentionedmethod of FIG. 5 or 8 may not satisfy requirements of different controlchannel signals.

On the other hand, as shown in FIG. 20, if a requirement of the lengthof the spreading/modulation sequence relaxes, the present invention cangenerate a control signal having a variety of requirements according toa Quality of Service (QoS) required for each control signal.

For example, a constant spreading length is applied in symbol units bythe spreading of an information symbol (for example, as shown in FIG.20, a spreading gain is “2”), the resultant symbol is multiplexed in afrequency domain and is then modulated by a specific scheme (e.g.,SC-FDM). Thereafter, as shown in FIG. 20, a time-domain sequence (e.g.,a time-domain sequence with the length “4”) is applied to each symbolunit (e.g., OFDM symbol) modulated in the frequency domain, so that thetime-domain modulation can be performed. The time-domain modulationsequence is multiplexed in the time domain as shown in FIG. 20, so thatthe length of a corresponding sequence may not be limited. In this case,the sequence applied to the information symbol is combined with theother sequence applied to the generated modulation symbol, so thatindividual UE signals can be distinguished from each other by thecombination of the two sequences.

If the used sequences have no problem in scalability (i.e., if across-correlation value between a short-length sequence and along-length sequence is low), the length of each sequence may havedifferent values in the same frequency/time resource area.

Otherwise, if the used sequences have the problem of scalability, it ispreferable that they may use the same structure (e.g., the same-lengthcombination) on the same resources.

In this case, a variety of sequences can be available, for example,Walsh, CAZAC, or pseudo-noise (PN) sequences. Preferably, the PNsequence may be adapted to solve the above-mentioned scalabilityproblem. Otherwise, a cross-correlation between used sequences havingdifferent lengths is firstly considered, and there may be proposed amethod for using only some combinations having no correlation problemeven when the sequences having different lengths are mixed with eachother (e.g., in the case of using the CAZAC sequence).

In the meantime, according to a modified example of the embodiment ofFIG. 8, the length of a spreading sequence applied to each informationsymbol may have different lengths in the same area.

In FIG. 20, the information-unit spreading of an information symbol in afrequency domain uses a spread sequence with the length of 2. However,if required, the length of the spreading sequence applied to each symbolhas no need to always have the same value, and may have different valuesaccording to individual information symbols. In this way, the spreadinggain is differently established in symbol units, so that eachinformation symbol may have different BER requirements.

Under the condition that the spread sequence applied to each informationsymbol is configured in the form of a combination of different lengths,if a cross-correlation value between sequences having different lengthsis high, users (i.e., UEs) may always use the same combination.Otherwise, if the cross-correlation value between sequences havingdifferent lengths is low, users (i.e., UEs) may use differentcombinations. The above-mentioned two cases can be properly allowed.

FIG. 21 is a conceptual diagram illustrating a method for spreading aninformation symbol in symbol units in a time domain, performing amodulation process in each domain by multiplexing atime/frequency-domain modulation/masking sequence, and transmitting atransmission (Tx) signal according to the modulated result.

The embodiment of FIG. 21 relates to a method for applying aninformation symbol on a time axis, differently from the above-mentionedembodiment of FIG. 20. In this case, a sequence on the frequency axis(hereinafter referred to as a frequency-axis sequence) is adapted toacquire the spreading gain (i.e., multi-user interference MUI removal).In FIG. 21, the spreading is performed in symbol units before aninformation symbol is applied on a time axis.

Provided that an actual transmission unit is fixed to a specific timelength (e.g., TTI), although an information symbol is applied while thespreading effect is given on a time axis, the amount of information tobe transmitted is reduced due to the fixed time length.

On the other hand, although the transmission unit is fixed to the TTI,the embodiment of FIG. 20 can adjust the length for a frequency axis, sothat the amount of information to be transmitted is changed. Namely, inorder to allow more UEs to transmit more information within the samespace, the present invention must increase the amount of resources onthe frequency axis.

According to the embodiment of FIG. 21, the amount of information islimited. However, if the embodiment of FIG. 21 increases thefrequency-axis length, it can accommodate more UEs therein. The numberof supportable UEs is determined according to categories of a usedsequence. For example, if only the same root sequence is used in theCAZAC case, a maximum number of supportable UEs are determined by thelength of channel delay spread.

In association with FIGS. 20 and 21, although the above-mentionedembodiments have disclosed that information symbols are applied toeither the time domain or the frequency domain, there is no need for anapplication area of the information areas to be fixed at either one ofthe two domains. Namely, the transmission signal generation methodaccording to the present invention can transmit information symbols toboth the frequency domain and the time domain. In this case, the amountof information to be transmitted increases whereas the spreading gainand the number of supportable UEs are decreased. In order to solve theabove-mentioned problem, resources are extended to the frequency/timeaxis to construct a control channel.

Next, a general method for supporting a variety of control channelformats will hereinafter be described.

In order to support a variety of control signal formats, two accessschemes (i.e., first and second access schemes) can be used.

The first access scheme sets the same control signal channel structureand adjusts data loaded on this channel structure. In other words, ifthe amount of loaded information is changed, a code rate is alsoadjusted to be suitable for the changed amount of loaded information.

The second access scheme defines a control channel structure accordingto a control channel format, and uses the defined control channelstructure. This second access scheme may also be classified into a firstmethod and a second method. The first method allows several UEs to sharepositions of resources to be re-used by the control channel. The secondmethod defines different resources to transmit a control signal, anduses the defined resources.

Firstly, if the control signal channel having a fixed size is used, atotal number of symbols are limited while a modulation symbol enteringeach “Information Symbol” position of FIGS. 20 and 21 is generated. Inmore detail, since the number of generated symbols is limited, only aspecific control signal format should be used, so that the modulationsymbol can be applied to the information symbol positions of FIGS. 20and 21. Otherwise, although control signal formats of different lengthsare used, the number of modulation symbols of a control signal must befixed at a predetermined value, so that the modulation symbols can beapplied to the information symbol positions of FIGS. 20 and 21.

In order to implement the above-mentioned operations, the channel codingrate may be adjusted as shown in FIG. 22, or the spreading gain may alsobe adjusted.

FIG. 22 shows an example for applying control signals of various formatswhen the size of a control signal channel is fixed according to oneembodiment of the present invention.

According to the embodiment of FIG. 22, the present invention may applydifferent coding rates, spreading factors, rate matching operations tocontrol signals of different lengths, so that the control signals can beadjusted to be suitable for a fixed control signal channel size.Therefore, a control signal symbol suitable for a corresponding controlsignal channel size can be generated. The present invention can usecontrol signals of different formats using the above-mentioned method,and can support different BER/FER performances required for individualcontrol signals.

Next, a method for reconstructing a control signal channel structureaccording to the uses of the control signal channel structure willhereinafter be described.

As shown in FIGS. 20 and 21, if the control signal channel structure canbe reconstructed according to its uses, the number of transmittableinformation symbols can be adjusted.

For example, if the structure of FIG. 20 transmits individualinformation symbols without spreading them, as many information symbolsas the number of sub-carriers can be transmitted. However, if thespreading factor of each information symbol increases in the order of 2,3, and 4 . . . , the number of transmittable information symbols isdecreased in proportion to the spreading factor.

The technique of FIG. 22 can be adapted to generate an informationsymbol corresponding to a control channel length. For example, thenumber of information symbols of an ACK/NACK signal is low (e.g., 1 or2), and the spreading can be performed for a long period of time, sothat high BER/FER requirements can be satisfied. Otherwise, if manyinformation symbols are required as in a CQI/PMI signal, the spreadinglength is reduced and the number of information symbols increases, sothat large amounts of bit information can be transmitted according tothe slightly-weakening BER/FER requirement.

The above-mentioned method for generating a control channel by adjustingthe spreading gain has an advantage in that it has a length-variableperformance via a single structure. However, this method must considerthe mixing of different UEs and the influence of interference caused byother cells.

In the case of transmitting a control signal by sharing the sameresources, a method for removing an interference between different UEsignals or signals of other cells will hereinafter be described.

This embodiment can establish the spreading gain of each symbol,irrespective of categories of the spreading/scrambling sequenceassociated with the information symbol. In other words, the spreadinggain of each symbol is exemplarily set to “2” in FIGS. 20 and 21. If auser or UE desires to adjust the number of transmission informationsymbols, the spreading gain applied to each symbol can be adjusted.Therefore, the present invention can properly define the number oftransmission information symbols using the combination of sequenceshaving different spreading gains for each control signal format, andtransmits the defined information symbols.

However, the above-mentioned scheme may unexpectedly generate either theinterference between different UEs which transmit signals using the sameresources, or the interference between signals of different cells.

Therefore, in order to adjust the spreading gain for each symbol,coordination of sequence use may be required. In other words, theabove-mentioned scheme may allocate sequences to be used by differentUEs within a specific cell, resulting in the prevention of interferencebetween the UEs. And, even in the neighboring cell, the above-mentionedscheme may perform coordination or randomization so as to prevent theinterference between sequences.

One of various methods for the above-mentioned operations is thesequence hopping. However, if sequences of different lengths are appliedto the spreading for each symbol as described above, the interferencemay be intensified. As a result, it is preferable that the number ofcombinations of the spreading sequences may be set to “1” only.

If required, a method for re-adjusting the information symbol itself maybe considered. In other words, the most basic spreading-sequencecombination is configured, UEs are discriminated by a combinationbetween sequence- and shift-indexes associated with the configuredcombination. Preferably, the spreading gain within each UE may beadjusted by changing a current information-symbol generation method toanother method.

FIG. 23 is a conceptual diagram illustrating a method for defining aspread format based on a control signal format within each UE accordingto the present invention.

In order to distinguish a first interference between UE from a secondinterference between neighboring cells, the adjustment between the firstand second interferences is required. For this purpose, the use ofsequences must be restricted, and a sequence to be used by each UE mustbe adjusted. In this case, if this part associated with theabove-mentioned adjustment is changed, the random-sequence hoppingscheme is required for the actual implementation of the presentinvention. Therefore, in the case of a UE specific sequence combinationpart, the present invention allows this UE specific sequence combinationpart to have no variation in connection with the control signal format,and changes only a method for generating the information symbol toanother method. A detailed description thereof will hereinafter bedescribed.

In more detail, the left side of FIG. 23 shows that each informationsymbol of FIG. 20 or 21 is mapped to each spreading sequence, and theright side of FIG. 23 shows that a single control channel specificspreading layer is additionally inserted in the center part of theleft-side structure of FIG. 23.

In this way, in the case of adjusting the spreading gain and the numberof information symbols using the above-mentioned additional spreadinglayer, the present invention can discriminate between UE signals withoutusing the UE specific sequence combination, so that it can freelyperform the cell planning, adjustment, and hoping operations and canalso freely define different control channel formats. Specifically,although resources are extended in the direction of a resource axis(i.e., time/frequency axis) where information symbols are loaded, thepresent invention can easily provide the scalability about theinformation symbols. A sequence to be used in the control channelspecific layer may be an arbitrary sequence. In order to remove noise orprevent the remaining interference caused by other UEs or other cells,it is preferable that sequences having a superior orthogonal propertymay be used in the present invention.

Next, a method for defining different resources in a control channel,and transmitting control signals over the control channel according tothe present invention will hereinafter be described in detail.

If the number of information symbols for each control signal format isfixed at the same number (i.e., if each control signal format has thesame number of information symbols), the information symbols arecommonly transmitted to the same resources. Otherwise, an additionalarea is defined so that this additional area is adapted to transmit theinformation symbols.

Namely, if it is determined that the number of generated informationsymbols is changed, the present invention defines another resource area,so that there is no need to consider the interference to be generatedbetween different formats. The interference within a cell or theinterference between different cells can be removed by the adjustmentprocess or can be maintained at a low value. However, the presentinvention must define an additional control channel for a correspondingformat, irrespective of the number of UEs used for the above format, sothat it has difficulty in effectively using resources.

According to the resource definition for different formats, the presentinvention may define different resource blocks in predeterminedallocation units on a frequency axis (for example, in the case of the3GPP LTE, 12 sub-carriers are defined as a single resource block (RB),and a sub-carrier is allocated using the defined RB as a basic unit.However, this scheme cannot define effective resources.

On the other hand, in the case of applying the spreading gain or thescrambling using the sequences of FIG. 20 or 21, the present inventionprefers to distribute resources according to the sequence-generationfacility and property. In more detail, if the CAZAC sequence is used asa basic unit, it is preferable that a basic unit of thespreading/scrambling sequence is set to a prime number. For thisoperation, in the case of supporting another control signal format byfrequency-axis division, the present invention performs a sub-carrierdivision, so that the number of sub-carriers contained in a specificpart, to be used as resources for the control signal, may be set to aprime number according to the sub-carrier division result.

In association with the above-mentioned description, a representativeexample has been described in Korean Patent Application No.2007-0032725, filed on 3 Apr. 2007, by the same applicant as the presentinvention, and entitled “METHOD FOR TRANSMITTING/RECEIVING SIGNAL BASEDON PRIME-NUMBER SEQUENCE”, which is hereby incorporated by reference. Inthe case of this example (hereinafter referred to as the ″32725 patent),sub-carriers contained in a predetermined number of resource blocks(RBs) are divided into a predetermined number of channels includingprime-number subcarriers, so that a signal is transmitted over thedivided channels. Therefore, the above-mentioned example guarantees thenumber of available sequences, so that a multi-cell structure can beeasily configured.

In association with the above-mentioned ″32725 patent, anotherembodiment will hereinafter be described in detail.

Another embodiment of the present invention relates to a method forproviding a channel structure to guarantee a maximum of spreadingsequences used for supporting a multi-cell environment, andtransmitting/receiving a signal via the channel structure. When theSC-FDM is maintained and at the same time a multi-access condition isprovided, the control channel structure according to this embodiment cangenerate a maximum of sequences, which can be distinguished from eachother without performance deterioration.

A method for generating a Zadoff-Chu (ZC) sequence serving as a CAZACsequence can be represented by the above-mentioned equations 1 and 2, aspreviously stated above.

Provided that the length to be applied to a system employing the CAZACsequence is set to “L”, and “N” of Equation 1 or 2 is equal to “L”(i.e., N=L) irrespective of the L value, the following problem mayoccur.

For the convenience of description, the CAZAC sequence of the length “L”has the following characteristics. If “L” is not set to a prime number,a generated CAZAC sequence may have a plurality of sequence IDs (i.e.,M=1, 2, . . . , L−1), but it should be noted that an unexpectedduplicate code may occur in the generated CAZAC sequences. In fact, thenumber of different codes is less than “L−1”. Otherwise, if “L” is setto a prime number, (L−1) different codes (i.e., the number of differentcodes is “L−1”) are generated.

In brief, in the case of using the CAZAC sequence including the ZCsequence, if a sequence length “L” is set to a prime number, the largestnumber of sequences can be used. Otherwise, if the sequence length “L”is not set to the prime number, the present invention can generatedistinctive sequences in association with another value “M”, which isdisjoint of “L”. Therefore, in order to guarantee a sufficient number ofsequences, it is preferable that the sequence length may be set to aprime number.

Presently, according to the 3GPP LTE, the control channel shown in FIG.3 has been adapted to transmit only a control signal other than data. Inthis case, a basic allocation unit allocated to a signal is called aresource block (RB), and the number of sub-carriers contained in one RB(i.e., 1 RB) is 12, which is not a prime number.

Generally, if the spreading sequence is applied to a frequency domain,the number of available sequences is determined according to the numberof used sub-carriers, so that the present invention determines whether amulti-cell environment can be supported. As described above, in order toapply the sequence in units of a resource block (RB) includingsub-carriers, the number of which is not a prime number, the presentinvention may use the following methods.

Firstly, a method for generating a prime-length sequence longer than arequired length, truncating the length longer than the required length,and employing the truncated sequence will hereinafter be described.

FIG. 24 is a conceptual diagram illustrating a sequence generationmethod according to a truncated-sequence generation method.

Referring to FIG. 24, if the length required for a system is not a primenumber, a prime number “X” higher than “L” is set to “N” of Equation 1or 2, so that sequences are generated. Thereafter, a sequence longerthan “L” from among the generated sequences is truncated to “L”.

According to the aforementioned truncated-sequence generation method,the number of sequences can be increased. However, the resultantsequence generated by the above-mentioned method may deteriorateCAZAC-sequence correlation characteristics due to the partialtruncation. In fact, if a specific sequence having poor correlationcharacteristics is removed from the generated sequences, the presentinvention is confident does not the number of sequences will be always“L−1”. And, the generated CAZAC sequences are partially truncated, sothat an unexpected deterioration may occur even in the property of aCAZAC sequence having a low PAPR (i.e., a low-PAPR CAZAC sequence).

Secondly, in order to solve the above-mentioned problem, the method ofFIG. 24 selects a maximum prime-number length “X”, which is equal to orless than the required length “L” of the communication system, generatesCAZAC sequences according to the selected result, and inserts a paddingpart in the part having the length “L−X”. For the convenience ofdescription and better understanding of the present invention, theabove-mentioned scheme is hereinafter referred to as a padding-typesequence generation scheme.

FIG. 25 is a conceptual diagram illustrating a method for generating asequence according to a padding-sequence generation scheme.

According to the padding-type sequence generation scheme, if therequired length “L” of the system is not a prime number, the highestprime number “X” from among several prime numbers, each of which is lessthan “L”, is set to “N” of Equation 1 or 2, and the sequence generationis performed. Thereafter, a part of a predetermined length C2 equal to“L−X” in the generated sequence length C1 is padded with “0”, so thatthe sequence of the length “L” is generated.

In the case of using the above-mentioned padding-type sequencegeneration method, a correlation part of a corresponding sequence is setto the part “C1” of FIG. 25, and then a sequence distinction is made. Asa result, the padding-type sequence generation method may prevent theoccurrence of correlation characteristics caused by the sequencetruncation. However, the sequence length for use in the above-mentionedpadding-type sequence generation method has the part C2 padded with “0”,so that correlation and PAPR characteristics may be deteriorated.

Finally, although the required length “L” of the system is not a primelength, the number of distinctively-generated sequences may be verysmall. However, if the sequence is directly generated with the sequencelength to be used, the correlation property between sequences or thesignal uniformity (e.g., PAPR, or cubic metric) in time and frequencydomains are further improved.

Therefore, the present invention provides a method for establishing acontrol channel structure advantageous to a guarantee of sufficientsequences, so that it can normally transmit/receive Tx control signalseven when no data exists in multi-cell environments. This method issuperior to the conventional method in which a sequence generation isadjusted to be suitable for a channel that does not have a prime-numberlength.

Namely, as described above, in order to improve the CAZAC-sequencecharacteristics (specifically, ZC-sequence characteristics), thefollowing items must be considered while a control signal channel isgenerated. Firstly, there is a growing tendency that the number ofsub-carriers is equal to the sequence length, so that it is preferablethat the number of sub-carriers of a single control signal channel maybe a prime number.

In brief, provided that the sequence length is a prime number as in theCAZAC sequence, and a control signal is transmitted using sequencesadvantageous to a guarantee of sufficient sequences, the presentinvention divides a corresponding control channel into a predeterminednumber of channels, each of which includes prime-number sub-carriers(i.e., the number of sub-carriers is a prime number) contained in apredetermined number of RBs. Therefore, the signal transmission methodaccording to the present invention can transmit/receive a correspondingsignal using the above-mentioned sequence via the divided channelincluding the prime-number sub-carriers.

Next, if an uplink of the SC-FDM communication system prescribed in the3GPP LTE transmits a control signal other than data, a detaileddescription of the above-mentioned embodiment will hereinafter bedescribed with reference to the control channel structure of FIG. 3.However, it should be noted that a detailed control channel structureand associated signal transmission/reception methods are not limited toonly the above-mentioned structure, and can also be applied to otherstructures, as readily understood by those skilled in the art.

FIG. 26 shows an exemplary structure in which controls channels causedby a resource block division are arranged at both ends of a systembandwidth on a one-to-one basis according to one embodiment of thepresent invention.

In FIG. 26, it is assumed that one or two physical resource block (PRBs)is allocated to a single physical channel, but it should be noted thatthree or more PRBs can also be applied to such a control channel withoutdeparting from the spirit or scope of the invention.

In more detail, provided that one or two PRBs (i.e., 1 or 2 PRBs) areallocated to the control channel, and 12 sub-carriers are contained inone PRB, these PRBs are divided into two control channels, each of whichincludes prime-number subcarriers (i.e., the number of subcarriers is aprime number) of various combinations, and then the resultant controlchannel is formed as shown in FIG. 26. As can be seen from FIG. 26, theresultant control channel is divided into two parts, and the dividedparts are arranged at both ends of the system bandwidth. In this case,the number of sub-carriers contained in one control channel is NA, andthe number of sub-carriers contained in the other control channel is NB.

TABLE 1 Control Channel BW N_(A) N_(B) 1PRB (12 sub-carriers) 1 11 5 7 75 11 1 2PRBs (24 sub-carriers) 1 23 5 19 7 17 11 13 13 11 17 7 19 5 23 1

In the meantime, FIG. 26 shows that two divided control channels(hereinafter referred to as two division control channels) shown inTable 1 are arranged at both ends of the system bandwidth, respectively.However, it should be noted that the two division control channels haveno need to be distributed to both ends of the system bandwidth.

FIG. 27 shows an exemplary structure in which a control channel causedby a resource block division is arranged at one end of a systembandwidth according to one embodiment of the present invention.

In FIG. 6, the control channel divided for the number of sub-carriers ofthe same combination may be arranged at both ends of the systembandwidth. Differently from FIG. 6, in FIG. 27, the control channel maybe arranged at only one end of the system bandwidth.

In association with FIGS. 26 and 27, the bandwidth (BW) allocated forthe control channel is divided into two control channels, but the numberof divided control channels may be determined in various ways accordingto system requirements.

In the meantime, if PRBs (e.g., some parts of one PRB divided intoseveral blocks) are arranged at both ends of the system bandwidth andare used as a control channel as shown in FIG. 26, or if divided controlchannels are arranged at one end of the system bandwidth as shown inFIG. 27, a symmetrical problem may occur. In other words, thesymmetrical problem indicates that the power is concentrated at only aspecific band contained in the system bandwidth.

For this operation, in the case of constructing a control channel, it ismore preferable that all PRBs (the number of PRBs is an integer) may bearranged at a transmission area of a control signal.

FIG. 28 shows an exemplary structure in which a predetermined number ofresource blocks are arranged at both ends of a system bandwidth and acontrol channel is formed by division of the resource blocks accordingto one embodiment of the present invention.

In FIG. 28, a predetermined number of PRBs (e.g., the number of PRBs isan integer) are arranged at both ends of the system bandwidth, and eachPRB is divided into control channels, each of which includes a primenumber of sub-carriers. In more detail, Ns1 PRBs (i.e., Ns1 number ofPRBs) and Ns2 PRBs (i.e., Ns2 number of PRBs) are arranged at both endsof the system bandwidth, respectively. And, the PRB region (Ns1) is usedas a control channel composed of (NA 1, NB 1) sub-carriers, and theother PRB region (Ns2) is used as a control channel composed of (NA2,NB2) sub-carriers.

In FIG. 8, the number of PRBs allocated for the control channels locatedat both ends of the system bandwidth may have the following combinationsshown in Table 2:

PRB for control channel Ns1 Ns2 1 1 0 0 1 2 2 0 1 1 0 2 3 3 0 2 1 1 2 03 4 4 0 3 1 2 2 1 3 0 4

If the number of PRBs allocated for the control channels at both ends ofthe system bandwidth is determined as shown in Table 2, both systembandwidths of FIG. 28 may be asymmetrical to each other.

For example, the size of one control channel area may be “xPRB”, and thesize of the other one control area may be “yPRB” (where x≠y). Therefore,the number of sub-carriers allocated to each control channel can bearbitrarily adjusted according to the number of PRBs allocated for thecontrol channel.

The process for generating control channels according to the number ofPRBs allocated for a control channel purpose within the system bandwidthcan be divided by the scheme of Table 1 according to the number ofsub-carriers given to each control channel. Needless to say, if thereare a large number of PRBs allocated for the control channel, the PRBsmay also be divided into three or more control channels. In this case,the PRB for each control channel is equal to the sum of severalprime-length control channels, instead of the sum of two prime-lengthcontrol channels.

The following Table 3 shows an example in which a predetermined numberof PRBs are divided into three control channels.

TABLE 3 BW for control channel N_(A) N_(B) N_(C) 1PRB (12 sub-carriers)2 3 7 2 5 5 2PRBs (24 sub-carriers) 2 3 19 2 5 17 2 11 11 3PRBs (36sub-carriers) 2 3 31 2 5 29 2 11 23 2 17 17

The sizes of individual channels generated by Table 3 may be exchangedas necessary. A predetermined number of PRBs allocated for the controlchannel may also be divided into four or more control channels.

In the meantime, if an actual system is implemented, as shown in FIGS.26 to 28, the system may not have only one control-channel-purposed PRBin one end of the system bandwidth.

FIG. 29 shows an exemplary structure in which a predetermined number ofresource blocks are grouped into several groups at both ends of a systembandwidth, the resultant groups are arranged at the both ends of thesystem bandwidth, and a control channel is formed by division of theresource blocks according to one embodiment of the present invention.

Referring to FIG. 29, a control-channel-purposed PRB located at each ofboth ends of the system bandwidth is composed of only a single controlchannel group, and may be grouped into a predetermined number of groupsin each area. In this case, the control channel having the structure ofFIG. 28 repeatedly appears. If the system bandwidth is large, a controlsignal can be transmitted via an arbitrary part contained in the systembandwidth.

In this way, each PRB group may be divided into a plurality of controlchannels, each of which includes a prime number of sub-carriers as shownin Tables 1 and 3. FIG. 29 shows that each group is divided into twocontrol channels.

Although the above-mentioned sequence generation/transmission methodaccording to the present invention has been exemplarily applied to theSC-FDM communication scheme, it should be noted that the scope of thepresent invention is not limited to the SC-FDM communication scheme andcan also be applied to the OFDM communication system as necessary.

It should be noted that most terminology disclosed in the presentinvention is defined in consideration of functions of the presentinvention, and can be differently determined according to intention ofthose skilled in the art or usual practices. Therefore, it is preferablethat the above-mentioned terminology be understood on the basis of allcontents disclosed in the present invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

For example, the method for generating/transmitting thetransmission-unit symbol according to the present invention can beapplied to a control channel for transmitting control information (e.g.,ACK/NACK) and a data channel for transmitting information in TTI or slotunits.

For another example, the present invention can transmit a control signalvia the channel designed by the inventive schemes disclosed in theembodiments. If the channel has a prime-number length, theabove-mentioned channel may also be adapted to transmit an arbitrarysignal indicating a sequence capable of easily guaranteeing sufficientsequences.

As apparent from the above description, the method forgenerating/transmitting a sequence based on a transmission unit in timeand frequency domains, the embodiments for supporting a variety offormats, and the method for transmitting a signal using a prime-lengthsequence can be equally applied to not only an uplink of the 3GPP LTEsystem based on the SC-FDMA scheme, but also a downlink based on ageneral OFDM scheme.

The present invention can be applied to not only the 3GPP LTE system butalso an arbitrary wireless communication system based on the OFDM schemeand/or the FDMA scheme.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method of transmitting, by a user equipmentincluding a processor and a transmitter, control information in acommunication system, the method comprising: multiplying, by theprocessor, a transmission information symbol s for the controlinformation by a frequency direction sequence c(k) to generate a firstoutput sequence s(k), where s(k)=s*c(k), k=0, . . . , N_(k)−1, and N_(k)corresponds to a number of subcarriers included in a resource blockallocated for an uplink control channel; multiplying, by the processor,the first output sequence s(k) by a time direction sequence x(n) togenerate a second output sequence s(k, n), where s(k, n)=s(k)*x(n), n=0,. . . , N_(n)−1, and N_(n) corresponds to a number of symbols used fortransmission of the control information in a transmission time interval;and transmitting, by the transmitter, the second output sequence s(k, n)through the uplink control channel in the transmission time interval. 2.The method of claim 1, wherein the time direction sequence x(n) is acell specific sequence.
 3. The method of claim 1, wherein thetransmission time interval is divided into two slots, and the controlinformation is transmitted in each of the two slots.
 4. The method ofclaim 3, wherein the control information is transmitted on differentfrequency bands in the two slots.
 5. The method of claim 3, wherein thefrequency direction sequence c(k) is configured to be different in thetwo slots.
 6. A user equipment for transmitting control information in acommunication system, the user equipment comprising: a processorconfigured to: multiply a transmission information symbol s for thecontrol information by a frequency direction sequence c(k) to generate afirst output sequence s(k), where s(k)=s*c(k), k=0, . . . , N_(k)−1, andN_(k) corresponds to a number of subcarriers included in a resourceblock allocated for an uplink control channel, and multiply the firstoutput sequence s(k) by a time direction sequence x(n) to generate asecond output sequence s(k, n), where s(k, n)=s(k)*x(n), n=0, . . . ,N₁−1, and N_(n) corresponds to a number of symbols used for transmissionof the control information in a transmission time interval; and atransmitter configured to transmit the second output sequence s(k, n)through the uplink control channel in the transmission time interval. 7.The user equipment of claim 6, wherein the time direction sequence x(n)is a cell specific sequence.
 8. The user equipment of claim 6, whereinthe transmission time interval is divided into two slots, and thecontrol information is transmitted in each of the two slots.
 9. The userequipment of claim 8, wherein the control information is transmitted ondifferent frequency bands in the two slots.
 10. The user equipment ofclaim 8, wherein the frequency direction sequence c(k) is configured tobe different in the two slots.